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BIO 315 > Module 11: Viral Pathogenesis (Types of Infection and Transmission) > Flashcards

Module 11: Viral Pathogenesis (Types of Infection and Transmission) Flashcards

1
Q

What 4 core challenges must all viruses face in order to persist?

A

1) Gain entry into permissive host cell

2) Acquire resources needed for replication

3) Evade host defenses

4) Spread to new hosts

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2
Q

Infection

A

The entry of a virus into a host cell

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3
Q

Infection is NOT the same as ____________

A

Infection is NOT the same as exposure

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4
Q

How do viral infection and exposure differ?

A

Infection = When virus actually gets INTO a cell

Exposure = When virus come into CONTACT with a cell

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5
Q

What are the 2 broad categories of infection?

A

Productive and Abortive

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6
Q

Productive Infection

A

Viral infection in which NEW viral particles are PRODUCED

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7
Q

Abortive Infection

A

Viral infection in which few to NO new particles are produced!

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8
Q

Infectious diseases occur during ____________ infections

A

Productive infections

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9
Q

The outcome of a viral infection depends on TWO interrelated activities, which are:

A

1) Replication of the virus

2) Host immune response

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10
Q

What are the 3 potential types of infection?

A

1) Acute Infection
2) Persistent (Chronic) Infection
3) Latent Infection

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11
Q

Acute Infection

A

Infection of SHORT duration

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12
Q

The majority of viral infections we experience are of what type?

A

Acute Infections

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13
Q

General process of an acute infection

A

1) Infection occurs

2) Signs/symptoms displayed

3) After a short period, infection is either cleared (most common) or causes host death

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14
Q

Why are acute infections described as a “disequilibrium”?

A

Because acute infections are dynamic: Both the host and virus experience continuous change throughout its duration

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15
Q

The severity of disease caused by acute infections depends on:

A

1) Rate of viral reproduction

2) Strength of immune response

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16
Q

What is an example of a virus that causes acute infection?

A

Rhinoviruses (picornaviridae family)

= Common Cold

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17
Q

What is the overall trajectory of a Rhinovirus infection?

A

1) Infection occurs (in upper respiratory tract)

2) Viral load + symptoms peak 2-3 days after initial infection event

3) Around 10 days after initial infection event viral load + symptoms have significantly decreased

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18
Q

Latent Infections

A

Infections in which the viral genome remains present in infected cells but viral replication only occurs sporadically

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19
Q

What is the overall process of a latent infection?

A

Typically occurs in ~3 “phases”:

1) Initial infection = period of acute replication

2) Viral replication stops = Latency period

3) Trigger event causes reactivation = viral reproduction resumes

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20
Q

Latency

A

Period of infection in which virus is PRESENT in a host cell but not actively replicating

(Just kind of there lying “dormant”)

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21
Q

Reactivation

A

(follows latency) The process of viral reproducting RESUMING

= Recurrence of acute infection signs and symptoms

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22
Q

What is the most well-studied mammalian virus that exhibits latency?

A

Herpesvirus (Herpesviridae family)

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23
Q

HSV =
HHV =

A

HSV = Herpes Simplex Virus
HHV = Human Herpes Virus

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24
Q

What virus causes cold sores + genital sores?

A

HSV I + II

(HHV-1 + HHV-2)

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25
What virus causes Chickenpox + Shingles?
Varicella Zoster Virus (VZV) (HHV-3)
26
What virus causes Kaposi Sarcoma (cancer in HIV patients)?
HHV-8
27
What virus causes Mononucleosis + Burkitt Lymphoma?
Epstein-Barr Virus (HHV-4)
28
All herpesvirus infections follow what infection trajectory?
1) Initial acute infection 2) Latency 3) Periodic reactivation
29
Episome
Extrachromosomal circular piece of viral DNA that exists and replicates within the nucleus of a host
30
LAT
Latency Associated Transcripts
31
What is the entire infection process and trajectory of HSV-1 infection?
**I. Acute Infection** 1) Primary infection; replication of virus occurs in mucosal cells at the site of infection 2) Newly produced viral particles enter local neurons and travel to the NUCLEUS **II. Latency** 3) HSV-1 uncoats to release viral DNA 4) Viral DNA forms an episome 5) LAT genes are expressed while ALL OTHER viral genes are repressed! **III. Reactivation** 6) Trigger event occurs causing expression of LAT genes to decrease and expression of other viral genes to increase 7) Viral replication resumes and assembled viral particles travel to the neuron periphery 8) Disease Symptoms occur
32
What trigger event causes HSV-1 to reactivate and exit latency?
Some stress event (though not totally clear) --> Reactivation is definitely tied to health of the host though
33
What are chronic infections AKA?
Persistent Infections
34
Persistent Infections
Infections in which viral particles are CONTINUOUSLY produced (in most cases for years after initial infection)
35
Persistent infections occur when the initial infection is not...
Not cleared within a "reasonable" amount of time
36
What is meant by: "Persistent infections require a balance between host and virus"?
The virus must replicate in the presence of the host's innate and adaptive immune responses
37
What are the 3 main suggested ways in which persistent infections are maintained?
1) Virus dampens immune response 2) Virus represses apoptosis 3) Mutations
38
How may viral-mediated immune response dampening lead to persistent infection?
Dampening the immune response of the host limits their ability to fight back and clear the virus == viral production "wins"
39
How may viral-mediated repression of apoptosis lead to persistent infection?
Repressing apoptosis keeps infected host cells alive, increasing the amount of viral production occurring! (The longer an infected cell stays alive, the more virus it can produce = longer duration of viral persistence)
40
How may mutations lead to persistent infection?
Mutations in either the host cell or virus may lead to persistent infections by altering the balance between host and virus
41
Reoviruses exhibit persistent infections due to...
Both host and viral mutations! **Host mutation** = Impacts cathepsin B (protease needed for uncoating = no uncoating, less viral production, less immune response) **Viral Mutation** = Impacts ability to undergo proteolytic uncoating
42
What is an example of a virus that causes persistent infections?
Reoviruses
43
Transmission
The spread of a virus from one host to another
44
What are the 3 main requirements of viral transmission?
1) Virus must **exit/be expelled** from initial host 2) Viral particles must **remain infectious** "between hosts" 3) Viral particles must **gain access** to appropriate cells in new host
45
What are the 4 main methods of transmission?
1) Horizontal Transmission 2) Vertical Transmission 3) Zoonotic Transmission 4) Mechanical Transmission
46
Horizontal Transmission
The transmission of viral particles from individual to individual WITHIN the SAME SPECIES
47
For horizontal transmission, the mode of entry into and exit from host cell are...
Exit and entry methods are **closely linked** (Ex: exit = coughing/sneezing, entry = inhaling expelled droplets)
48
What are the 3 main routes of horizontal transmission?
1) Respiratory 2) Fecal-Oral 3) Sexual
49
2 example viruses that are horizontally transmitted through respiratory route:
Rhinoviruses + Influenza
50
2 example viruses that are horizontally transmitted through fecal-oral route:
Poliovirus + Hepatitis A virus
51
2 example viruses that are horizontally transmitted through sexual route:
HIV + HPV
52
How is Ebola horizontally transmitted?
Via direct contact of mucous membranes or cut with contaminated body fluids (body fluids include: sweat, saliva, semen, urine, and vomit)
53
Vertical Transmission
The transfer of viral particles from MOTHER to OFFSPRING (fetus)
54
What are the 3 ways vertical transmission can occur?
1) **Mother --> Developing fetus** (via blood through placenta or during birth) 2) **Mother --> newborn** (via breastmilk) 3) Retroviruses only: Mother --> germ cells that become embryo
55
How is HIV vertically transmitted?
Via breastmilk OR by blood through the placenta or during birth
56
How is Rubella and Hepatitis C + B vertically transmitted?
Via blood during birth or through placenta
57
Germ cells
Gamete precursors (spermatocytes + oocytes)
58
How are retroviruses vertically transmitted?
Via germ cells!
59
Endogenous Retrovirus
Proviral DNA that is integrated into the DNA of host gametes that can subsequently be found in EVERY cell of a developing embryo
60
How are endogenous retroviruses "formed"?
By a retrovirus infecting a germ cell --> The gametes that infected germ cell give rise to will contain the proviral DNA
61
If an endogenous retrovirus infected gamete becomes part of a zygote, the resulting embryo will...
Have the proviral DNA of the endogenous retrovirus in ALL of its cells
62
What is an example of a virus that is spread via germ cells?
MMTV (Mouse Mammary Tumor Virus)
63
Is endogenous retrovirus transmission the main transmission method for retroviruses?
NO
64
What potential critical role do human endogenous retroviruses play? (What is the evidence?)
Human endogenous retroviruses may play an important role in our EVOLUTION --> ~5-8% of our genome is made up of Human endogenous retroviral DNA
65
HERV
Human endogenous retrovirus
66
Zoonotic Transmission
The spread of infectious disease BETWEEN species (Animal to human or human to animal)
67
Zoonosis
Diseases that are primarily present in animals but CAN be transmitted to humans
68
Reservoir Host
The species a virus NORMALLY exists/replicates in
69
Reservoir hosts serve as a ______________ for other organisms and are often ___________ to the pathogen
Reservoir hosts serve as a **source of infection** for other organisms and are often **tolerant** to the pathogen
70
In zoonotic transmission, human hosts are referred to as ___________ hosts Why?
Human hosts = **DEAD-END Hosts** --> because human-human transmission of zoonotic viruses almost NEVER occurs so viral spread "ends" once in a human host (Think about Rabies)
71
The reservoir host for most zoonotic viruses are...
Vertebrates
72
How do humans typically acquire zoonotic viruses?
Through the SALIVA of infected animals (when BITTEN)
73
What is an example of a virus that undergoes zoonotic transmission?
Rabies Virus
74
How are Ebolaviruses zoonotically transmitted?
1) Directly: Bat --> Human 2) Indirectly: Bat --> Primate --> Human
75
Zoonotic viruses may evolve into...
More typical human viruses
76
What is an example of a zoonotic virus evolving into a human virus?
HIV is an evolved form of SIV (Simian Immunodeficiency Virus) --> SIV infected a human and then overtime evolved ability to replicate efficiently in human cells + be transmitted human-human == HIV formed
77
Mechanical Transmission
VECTOR facilitated transfer of virus from host to host (Transmission via a "middle man"; vector)
78
In mechanical transmission the vector can be...
Living or NOT living
79
How is Ebola mechanically transmitted?
Via medical devices/tools contaminated with blood of infected individual
80
How is the Myxoma virus transmitted?
Via mechanical transmission using a PASSIVE vector --> Transmitted from rabbit to rabbit via fleas + mosquitoes
81
How is Yellow Fever virus transmitted?
Via mechanical transmission using an ACTIVE vector --> Transmitted from human to human via mosquitoes
82
Active vs Passive Vectors
Passive Vectors = Virus does NOT replicate within the vector Active Vectors = Virus DOES replicate within the vector
83
What are all the ways ebola virus can be transmitted?
1) Horizontal transmission --> a) via mucous membrane or cut contact with contaminated fluids --> b) via sexual transmission 2) Zoonotic transmission --> a) bat --> human --> b) bat --> primate --> human 3) Mechanical transmission --> via contaminated medical devices/tools

BIO 315 (29 decks)

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